1. Field of the Invention
The present invention relates generally to a vibration damping device for use in an automotive suspension system, and a suspension system using the device. More particularly, the present invention is concerned with such a vibration damping device equipped with a sensing member providing signals usable as sensor signals for control in a control system for vehicle driving conditions.
2. Description of the Related Art
With the goal of improving drive stability of automotive vehicles, mechanically assisted driver control has been studied as a way to reduce uncontrolled vehicle behavior, such as skidding. Specifically, antilock braking systems (ABS) has already come into use as means for preventing locking of the wheels during braking. Additionally, there are proposed vehicle control systems such as traction control, which reduces wheel spin during acceleration, or vehicle stability control, which affords overall control of stabilization of vehicle behavior.
These vehicle control systems as discussed above are typically carried out utilizing sensor signals of various kinds which reflect driving conditions of the vehicle. As one design for sensing such signals, there have proposed to date several mechanisms for sensing external forces acting on the wheels (road surface friction, vertical force, etc) or road surface frictional coefficient. These include, for example, the mechanisms taught in Citations 1, 2, and 3.                [Citation 1] JP-B-2628444        [Citation 2] JP-A-2001-191767        [Citation 3] JP-A-2002-316502        
Citation 1 teaches a mechanism constructed with a strain gauge embedded in a hole made in the axle. This mechanism, however, makes a practical implementation difficult owing to axle strength and construction as well as a low manufacturability. In actual practice, it would be necessary to make a number of holes the axle in order to be able to sense in a number of different directions, making practical implementation even more difficult.
Citation 2 teaches another mechanism constructed with sensed elements disposed in the tires, whereby tire deformation, rotation, or the like can be sensed from the outside. This mechanism, however, may possibly suffer from deterioration in tire performance owing to the added sensed elements that are disposed in the tire, as well as damage of the sensed elements by flying pebbles or mud thrown up from the road surface. While it is easy for this mechanism to sense wheel rotation speed, it is exceptionally difficult to calculate external force acting on a wheel using such sensor values.
Citation 3 teaches yet another mechanism constructed with a rim wheel elastically coupled to a disk part, whereby displacement of the rim wheel relative to the disk part is sensed by means of a position sensor or the like. In this mechanism, however, the need to elastically couple the rim wheel to the disk part would deteriorate a rigidity of the wheel per se, with adverse effects on driving stability. Additionally, since the sensor is disposed at a location very close to the tire, it is susceptible to be struck by a flying pebble or the like.